Copper alloy and process of producing and treating the same



Patented Feb. 7, l928.

UNITED STATES PATENT OFFICE.

MICHAEL G. COB8ON, OI JACKSON HEIGHT-8, nw YO, ABBIGNOB 1'0 ILIGIBO METALLURGICAL COMPANY, A CORPORATION OI W187. mom

COPPER ALLOY AND P300188 01' PRODUCING AND 'rxxa'rmo 'rnz IA.

80 brewing. Application ma September 38, 198i, Serial Io. ram, and in cm I'ebrury I1, 1.

The invention relates to the production of hard and strong allo s containin high ercentages of copper. t comprises eapp ication of certain processes of heat-treatment to copper or copper alloys in which certain chemical elements are present inregulated and preferably small amount; and as applied to materials in which such elements are not already present in suitable quantity, it comprises their preliminary addition to impart the ability to assume a hard and strong condition upon suitable heat treatment. The primary ob'ect of the invention is to increase the strength and hardness of the material treated, but in some cases another important object is to preserve or im rove certain other properties of the materia For example it may be desired to preserve the normal color of the material to be hardened, or to increase its resistance to corrosion, or to impair as little as ossible its ductility or electrical conductivity. The description will be confined for the most part to a discussion of the effect of the invention on hardness, but it will be understood that the hardening will be accompanied in general by an increase in strength, and that in,'some cases such increase is more important than the hardening.

I have found that copper and copper alloys containing suitable quantities of silicon and one or more of a group of metals referred to herein as hardening metals will assume a remarkably hard and strong condition if subjected to the heat treatment presently to be described. Experimental evidence as well as theoretical considerations indicate that the actual hardening efl'ect is due to silicides of definite composition. Furthermore it is indicated that the silicides which are most effective as hardening agents are present in the hardened material as discrete particles which are invisible under the microscope, from which it is concluded that they are present as ultramicroscopic crystals. The hardening efiect is ascribed, in consonance with a theory recently advanced b others, to the action of these hypothetical u tramicroscopic crystals in preventing the breaking down of the grains of the copper or copper alloy, the crystals serving to key together or interlock adjacent planes and thus reduce their tendency to slip one upon the other under the influence of externally applied stress.

The silicides which I have found to be most effective as hardening agents are those of chromium, cobalt, and nickel. The princip al effect appearsto be largely due to silicides in which about six wei hts of chromium, or about four weights 0 either cobalt or mckel, combine with one weight of silicon, corresponding approximately to the formula: Cr,Si, 00,81, and Ni,Si.

By adding the fore oing elements in suitable proportions, and y suitable heat treatment, copper can be prepared in which silicide exists either almost solely as microscopic cr stals, or almost solely in the form which I ave assumed to be ultramicroscopic crystals, or both varieties of silicide may be present in varying quantities. Upon examnation of the silicide-containing products it is found,- that the microsco ic crystals have only a slight hardening e ect Whereas the other form of the silicide has a very much greater hardening effect. Accordingly the invention in its preferred embodiment and where maximum hardening is desired contemplates that the quantity of silicide present in the copper shall be such, and the heat treatment shall be so controlled, that a maximum uantity of the variety of silicide which is the most effective hardening agent shall be produced.- It is preferred in some cases to add only so much of the components of the desired silicide as corre ends to the quantity of the silicide which it is possible to brin into the more effective form, n pothetical y the ultramicrosco ic crystalline form, and then to apply a eat treatment adapted to bring substantially all the silicide present into this form.

It will be understood that the invention is not dependent upon the correctness of the hypothesis that the effective hardening agent in material treated according to my invention is a silicide praent as crystals of ultramicroscopic dimensions, but as a matter of convenience in describing the invention such crystals will be referred to throughout the description as though their existence had been actually demonstrated.

My researches indicate that the maximum quantity of silicide which can be brought dicated as into the ultramicroscopic crystalline form in the metal is about 0.9% for the chromium silicide; about 2.0% for cobalt'silicide; and about 7.5% for the nickel compound. There are certain minimum quantities of the silicides which appear to be necessary before any ultramicroscopic crystals can be formed, quantities of SlllCldE less than these minima evidently remaining in solid solution despite heat treatment designed to precipitate them. The minima referred to are about 0.2% for chromium silicide; about 0.3% for cobalt silicide: and about 1.2% for nickel silicide. The incorporation into the metal to be hardened of silicides in quantities in excess of those which can be brought into the ultramicroscopic crystalline state by heat treatment is not precluded. Such excess quantities tend to form microscopic crystals and these have a hardening action through as mentioned above they are much less effective than the smaller crystals. The microscopic crystals have a much stronger effect than the ultramicroscopic in diminishing ductility, and it will therefore often be desirable to exclude them or to limit their quantity.

The chromium, cobalt or nickel and the silicon are not necessarily-incorporated in the exact proportions which have been inroducing the most effective hardening silicides. An excess of either one of the components of the silicide can be used. Excess chromium, if present in sufficient quantity, appears in the hardenedmetal as spherical microscopic crystals,

while excess cobalt and nickel are held by the copper in solid solution. The excess metal in each case exerts per se a slight hardening effect, but its most important effect is to alter the quantit of silicide which can be taken into solid so ution and precipitated therefrom as ultramicroscopic crystals during the heat treatment. In the case of chromium the solubility of the silicide is not materially chan ed, but excess cobalt diminishes the solu ility of the silicide while excess nickel strongl increases the solubilit of nickel silicide. ue to this effect of nicke cop er-nickel allo s containing as high as 40% i can be har ened by a propriate heat treatment after a content 0 silicon has been incorporated.

Silicon may also be present in excess of the quantity which will combine with the hardening metal. The excess will occur in solid solution in the hardened metal and has the effect of diminishing somewhat the quantity of silicide which can be taken into solid solution as a preliminary to precipitating it as ultramicroscopic crystals. Excess silicon has per se a slight hardenin effect. An excess of either silicon, cobat or nickel in solid solution in the hardened metal diminishes its electrical conductivity. Excess nickel, because of the large quantity which can be held in solid solution may 1iminish the conductivity enormously.

A suitable heat treatment for hardening the above-described compositions comprises holding the material at a high temperature until the hardenin metal and silicon have been completely taken up by the copper, or until the copper approaches saturation with these elements, quenching the material, and then holding it at a lower temperature for a sufiicient time for the silicide to precipitate in the desired form. The preferred range for the high-temperature homogenizing treatment is 750 to 975 C. Only a short period is required at these temperatures; the desired result will usual] be brought about within two hours, and thirty minutes or less is often sufficient, especially at the higher temperatures of the ran e given. The uenchin holds the bulk of the silicide in so id solution, and the quenched material is usually soft and suitable for any kind of cold work.

A second heat treatment wherein the silicide is caused to precipitate as ultramicroscopic crystals completes the hardening. The second heat treatment comprises heating the material to a temperature within the range of about 250 C. to 600 C. and holding it for a time. A few minutes suffice to produce the maximum hardening at 600 C. while many weeks may be required at 250 C. There is doubtless a tendency to hardening at still lower temperatures, but the action is too slow to be useful.

If the material is heated above 600 C. during this second heat treatment, the silicides precipitate as microscopically visible grainlets. As a general rule the ductility which accompanies a given hardness is greater the lower the hardening temperature. It has been observed, however, that when the hardening temperature is in the vicinity of 450 C. to 500 C., less ductility often accompanies a given hardness than when the hardening temperature is either higher or lower. To secure maximum ductility it is sometimes desirable to use the lower hardenin temperatures even though the duration of the heat treatment is considerably prolonged by so doing.

If the hardenin temperature does not exceed about 450 the material reaches its maximum hardness and then remains unchanged if the temperature is continued, but if the higher temperatures of the hardening range are employed an undue prolongation of the hardening temperature will result in the formation of silicide crystals of larger than optimum size, accompanied by a retrogression in hardness. This retrogression after the moment of maximum hardness is more pronounced the higher the hardening temperature.

Where it is desired to make wrought arti- IOU cles from material hardened according to my invention, for example an article shaped by drawing or forging, a variety of methods of procedure will suggest themselves and one can be chosen which is adapted to the particular conditions. Compositions accordmg to the invention may be hot worked without difliculty. When the quantity of silicide premnt is relatively high, for example above about 4% of nickel silicide, the hot-working should be accompanied by suflicient holding at homogenizing temperatures to keep the material in a sufliciently homogeneous condition. At the end of the hot work the silicide should be brought into solid solution, if it is not alread in that condition, b heatin to 750 .-975 C., and should e quenc ed from the temperature at which it is homogeneous whether this is incidental to the hot-workin operation or is the result of reheating. T e article is then in condition for cold-working or hardening in the manner already described. The hardened article may be subjected to a small amount of-cold work, still further enhancing its strength, but where such cold work is contemplated the hardening step should usually be discontinued before the material has acquired its maximum hardness. Cold work increases the hardness of the material but little. Severe cold work may soften the material, bringing it into a condition where in it resembles the annealed material.

I have produced copper hardened with chromium silicide having a Brinell hardness (500 kg. load, 10 mm. ball) higher than 100, and a tensile strength of 54,000 pounds per square inch which can be increased to 85,000 pounds per square inch by cold work. Using cobalt silicide the corresfilonding figures are 150 Brinell for her ess, 85,000 pounds per square inch for tensile strength as hardened, and 98,000 pounds per square inch as cold drawn. Cop er hardened with nickel silicide has recorde over 250 Brinell, over 110,000 pounds. r s uare inch tensile stren th as hardene an around 125,000 poun 5 er square inch when cold drawn. The bar ening effect of one per cent of silicide is greatest for the chromium compound and least for the nickel, but since nickel silicide is more soluble in copper than is cobalt silicide, and the latter is more soluble than chromium silicide, copper can be made harder with nickel silicide than with the cobalt compound, and harder with cobalt silicide than with chromium silicide as indi cated by the figures given above.

The invention can be applied in general to the alpha alloys of copper as these have the ability to take chromium. cobalt, or nickel silicides into solution at temperatures at which the alloys remain solid. Thus copper alloys containing for example 7% aluminum, or 8% tin, or 20% manganese, or 30% zinc, can be hardened with silicides, as these 9.110 s are of the al ha t pe. The solubility of tie silicides in t e so id alloy diminishes with increasing content of zinc or other alloyin metal, and less hardening is therefore possi le where the content of zinc or the like 18 higher. Also the melting point of a brass or bronze is considerabl less than that of copper, which further diminishes the quantity of silicide which can be caused to go into solid solution.

Manganese is a useful addition to materials to which in invention is applied, as it acts as a deoxi er and tends to prevent oxidation and loss of silicon. Under some conditions manganese and iron appear to form silicides w ich act as hardening agents, perhaps in a manner similar to that which as been described in connection with chromium, cobalt, and nickel. Iron and manganese, however, are very much less efl'ective as hardeners than the other metals referred to. The silicides of a plurality of the hardening metals may of course be used jointly in practising the invention.

It is well known that cobalt, nickel and silicon greatly increase the resistivity of copper if separately alloyed with it. As some of the compositions of my invention contain considera le quantities of cobalt or nickel or both, together with silicon, it might be ex ected that these compositions would exhibit rather high resistivities, but the resistivities are in fact much lower than might be predicted from the quantities of silicon and hardening metal resent. The total iiicrease in resistivity rought about by an addition of silicon accompanied by an addition of cobalt or nickel is not only less than the sum of the effects of the silicon and metal when added to separate lots of copper, but in some cases is actually much less than the effect of either the silicon or metal it added alone. This is true even when the copper containing both silicon and hardening metal is in the quenched condition and the additions are in solid solution,the state in which they increase resistivity most strong- 1%. If the additions are precipitated from t e solid solution, as in the hardening heat treatment, the conductivity is still further greatly increased.

The following example will illustrate this phenomenon. Copper containing 1.5% Si and no hardening metal has a reiistivity of the order of 16 inicrohins per centimeter cube. Copper containing 6% Ni and no silicon has a resistivity of about 21, measured in the same unit But copper containing 6% Ni and 1.5% Si has a resistivity of only 9 or 10 microhms per centimeter cube as quenched, and this value may be reduced to 4.9-5.2 microhms per centimeter cube by the described hardening treatment, For a given total content of silicon and hardening metal,

the conductivity reaches a maximum when the silicon and hardening metal are resent in about the proportions correzpon 'n to the silicides for which formulae have can given. The unexpectedly low increase in resistivit which accompanies the simultaneous ardition of silicon and nickel may perhaps be explained b the theory that these elements tend to eform the crystal lattice of copper in opposite directions, the atomic volume of copper being intermediate those of nickel and silicon.

Copper hardened according to the invention with cobalt and silicon in amounts equivalent to about 3% Co si ma have a resistivity as low as 2.9 to while if the hardening additions correspond to about 1% Cr,Si, the resistivity may be as low as 2.0, pure copper beins. 1.75.

By the practice of the invention there ma be produced a class of useful materia which to the best of my knowledge have not heretofore been prepared. This class of materials may be defined as tho e containing at least 93% copper, having good workability, and a conductivity of at least 35%; and in a condition free from cold-working strains having a hardness of at least 150 Brinell and a tensile strength of at least 95,000 ounds per square inch. A more restricteci class of..new and useful materials contain at least 97% copper, are readily workable, have a conductivity of at least 55%, and, withoutcold work, are above 135 Brinell in hardness and above 80,000 pounds per square inch in tensile strength. Finally, for use where nearly pure copper of high conductivity is required and considerable hardness and strength are desired, the invention is capable of roducing a class of materials of good wor ability with copper at least about 98.5%, and conductivity at least testin without previous cold work at least rinell and at least 50,000 pounds per square inch.

I claim:

1. A rocess which comprises subjecting a material consisting redominantly of copper and containing silicon and a metal having the hereindescribed hardening effect of chromium, cobalt and nickel to an homogenizing treatment at high temperature, thereby bringing substantial quantities of silicon and hardening metal into solid solution; quenching; and then heating the material at a temperature between about 250 C. and about 600 C. for a sufiicient period to develop a substantial pro ortion of the hardness attainable at sue temperature; and finally cooling the material.

2. A rocess which comprises bringing a materia consisting predominantly of copper, and containing sllicon and-a metal havmg the hereindescribed hardening effect of chromium, cobalt and nickel, to a temperature below 600 C. and "into a condition wherein it contains substantial quantities of s licon and hardening metal in solid solution; heating the material at a temperature between about 250 C. and about 600 C. for a suflicient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

3. A process which comprises bringing a material consisting predominantly of copper, and containing silicon and a metal havmg the hereindescribed hardening effect of chromium, cobalt and nickel, to a tem rature below 600 C. and into a con ition wherein it contains substantial quantities of silicon and hardening metal in solid solution by the steps of heating the material at a tem erature between 750 C. and 975 C. and t en quenching it; heatin the material at a temperature between a out 250 C. and about 600 C. for a sufficient period to develop a subzztantial proportion of the hardness attainable at such temperature; and finally cooling the material.

4. A process which comprises adding silicon and a metal having the hereindescribed hardening effect of chromium, cobalt and nickel, to a material consisting predominantly of copper; bringin the material so prepared to a temperature below 600 C. and into a condition wherein it contains substantial quantities of silicon and hardening metal in solid solution; heating the material at a temperature between about 250 C. and about 600 C. for a sufiicient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

5. A process which comprises adding silicon and a metal having the hereindescribed hardening effect of chromium, cobalt and nickel, to a material consisting predominantly of copper; bringing the material so prepared to a temperature below 600 C. and 1nto a. condition wherein it contains substantial quantities of silicon and hardening metal in solid solution, by the steps of heating the material at a temperature between 750 C. and 975 C. and then quenching it; heating the material at a temperature between about 250 C. and about 600 C. for a sufiicient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

6. A process which comprises brin ing a. material consisting predominantly o copper, and containing substantial quantities of silicon and a metal having the hereindescribed hardening effect of chromium, co balt and nickel, to a temperature below 600 C. and into a condition wherein it holds in solid solution substantially all of the silicon and hardening metal present; heating the material at a temperature between about 250 C. and about 600 C. for a sutlicient period to develop a substantial proportion of the hardnes attainable at such temperature; and finally cooling the material.

7. A process which comprises bringing a material consisting predominantly of copper and containing substantial quantities of silicon and a metal having the hereindescribed hardening effect of chromium, cobalt and nickel, to a temperature below 600 C. and into a condition wherein it holds in solid solution substantially all of the silicon and hardening metal present by the steps of heating the material at a temperature between 750 C. and 975 C. and then quenching it; heating the material at a temperature between about 250 C. and about 600 C. for a sutlicient period to develop a substantial pro ortion of the hardness attainable at such temperature; and finally cooling the material.-

8. The process which comprises adding silicon and a metal having the hereindescribed hardening efiect of chromium, cobalt and nickel, to a material consisting predominantly oi copper; bringing the material so prepared to a tem erature below 600 C. and into a condition wherein it holds in solid solution substantially all of the silicon and hardening metal present; heating the material at a temperature between about 250 C. and about 600 C. for a 'sufiicient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

9. A process which comprises adjusting the composition of a material consisting predominantly of copper so that it will contain in substantial quantities the constituents of at least one of the hereindescribed group of hardening silicides, in substantially the proportions in which they occur in said silicides; bringing the material to a temperature below 600 C. and into a con dition wherein it holds in solid solution substantially all of the silicon and hardening metals present; heating the material at a temperature between about 250 C. and

about 600 C. for a sufficient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

10. A process which comprises adjusting the composition of a material consisting predominantly of copper so that it will contain in substantial quantities the constituents of at least one of the hereindescribed group of hardening silicides, in substantially the proportions in which they occur in said silicides; bringing the material to a temperature below 600 C. and into a condition wherein it holds in solid solution substantially all of the silicon and hardening of the hardness attainable at such temperature; and finally cooling the material.

11. A process which com rises adjusting the composition of a materia consisting predominantly of copper so that it will contain in substantial quantities the constituents of at least one of the hereindescribed group of hardening silicides, in substantially the proportions in which they occur in said silicides; bringing the material to a tem erature below 600 C. and into a con 'tion wherein it holds in solid solution substantially all of the silicon and hardening metals present; heating the material at a temperature between about 250 C. and about 600 C. for a suflicient time to develo substantiall the maximum hardness attainable at suc teniperature; and finally cooling the materia 12. A process which com rises adjusting the composition of a materia consisting predominantly of copper so that it will contain in substantial quantities the constituents of at least one of the hereindescribed group of hardenin silicides, in substantially the proportions in which they occur in said silicides; bringing the material to a tem erature below 600 C. and into a condition w erein it holds in solid solution substantially all of the silicon and hardening metals prescut, by the steps of heating the material at a temperature between 750 C. and 975 C. and then quenching it; heating the material at a temperature between about 250 C. and about 600 C. for a suificient period to develop substantially the maximum hardness attainable at such temperature; and finally cooling the material.

13. A process which comprises adding to commercially pure copper substantial quantities of the constituents of at least one of the hereindescribed group of hardening silieides in their approximate combining proportions; bringing the material so prepared to a temperature below 600 C. and into a condition wherein substantially all of the silicon and hardening metal are held in solid solution; heatin the material at a temperature between a out 250 C. and about 600 C. for a sufiicient period to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

14. A process which comprises subjecting a material consisting predominantly of copper containing silicon and nickel, to an omogenizing treatment at high temperature, thereby bringing substantial quantities of silicon into solid solution; quenching;

and then heating the material at a temperature between about 250 C. and about 600 C. for a sufiicienhperiod to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

15. A process which comprises bringing a material consisting predominantly of copper containing silicon and nickel, to a tem erature below 600 C. and into a con 'tion wherein it contains substantial quantities of silicon and nickel in solid solution; heating the material at a temperature between about 250 C. and about 600 C. for a sufiicient pe riod to develop a substantial proportion of the hardness attainable at such temperature; and finally cooling the material.

16. A process which comprises adjusting the composition of a-material consisting pre dominantly of copper so that it will contain in substantial quantities the constituents of at least one of the hereindescribed group of hardening silicides. in substantially the roportions in which they occur in said silicides, whereby the material becomes adapted for hardening by the hereindescribed heat treatment.

17. A rocess which comprises adding to commercially pure copper substantial quantities of the constituents of at least one of the hereindescribed group of hardening Hillcides in their approximate combining proportions, whereby the cop er becomes adapted for hardening by t e hereindescribed heat treatment.

18. A process which comprises subjecting a material consisting predominantly of copper containing silicon and nickel to an iomogenizing treatment at high temperature, thereby bringing substantially all of the silicon and nickel present into solid solution; quenching; and then heating the material at a temperature between about 250 C. and about 600 C. for a suflicient period to develop substantially the maximum hardness attainable at such temperature; and finally cooling the material.

19. A new; material consisting principally of copper and containing substantial quantities of the constituents of at least one of the hereindescribed group of hardening silicides; having good workability, a conductivity of at least and, in a condition wherein it is free from cold-work strains, a

Brinell hardness of at least 150, and a tensile strength of at least 95,000 pounds per square inch.

In testimony whereof, I aflix my signature.

MICHAEL G. CORSON. 

